1. Field of the Invention
This invention relates to a head drum apparatus for a video tape machine and is particularly concerned with reducing clogging of the head.
2. Description of the Prior Art
Japanese Utility Model application JP-A-23224/1984 discloses a head unit of a video tape recorder which can be vibrated in order to reduce clogging of the head unit. As shown in FIGS. 6 and 7 of the accompanying drawings, the known head unit 12 is mounted on a rotary drum 4 around which is wound a magnetic recording medium in the form of a tape 19. The head unit 12 is provided with a mounting element 13 mounted on the drum 4 by a screw. An exciting element 15 is mounted on the mounting 13, and in turn a head tip 14 is mounted on the exciting element 15. The tip end of the head tip 14 projects slightly from the rotary drum 4 so as to contact the tape 19. The head tip 14 has a head gap, and signals can be read from and written on the tape 19 by the head tip 14.
The exciting element 15 is electrically connected to an ultrasonic signal generator and is arranged so that the head tip 14 is vibrated in a direction radially of the drum, i.e. towards and away from the tape 19 as shown by arrow B in FIG. 7.
The ultrasonically vibrating head tip 14 shakes off foreign matter (mainly, bonding material and magnetic powder separated from the tape) attached thereto, and seeks to prevent read and write failure, or dropout, due to clogging of the head gap.
The resonant frequency of the exciting element 15 is determined by the Young's modulus thereof and the mass of the head tip 14 as a load. Typically, the head tip 14 has a frequency as low as 15 to 20 kHz, and in such case the head tip 14 cannot sufficiently shake off the foreign matter attached thereto. As a result, dropout can still occur in reading or writing of the signals.
Moreover, the head tip 14 vibrates in the direction towards and away from the tape 19. Therefore, problems may arise due to poor tape-contact between the head tip 14 and the tape 19, or a speed error in the rotation of the head. Also the head tip 14 is secured on the exciting element 15 in the form of a piezoelectric element which is unstable in the sense that it tends to shift the position of the head tip 14 with variations in temperature. This can cause tracking errors of the head.